In recent years, global warming due to an increase in concentration of carbon dioxide gas in the atmosphere is becoming a global issue. Active efforts have been made in various industrial fields aiming to develop techniques for reduction in carbon dioxide gas release to the atmosphere. In the field of plastics production, plastic products have been conventionally produced from general-purpose oil-derived input materials and, after use, their waste is processed by incineration etc., resulting in discharge of carbon dioxide gas into the atmosphere. In recent years, attention is focused on plastics produced from plant-derived materials, which originate from carbon (carbon dioxide gas) in the atmosphere. In particular, research and development has been actively performed towards developing practical polylactic acid based materials, which are generally high in transparency and relatively advantageous in terms of cost as well.
Among other biodegradability plastics, polylactic acid has a relatively high glass transition point of about 57° C. as well as high rigidity, and it is now drawing attention as alternatives to materials such as polyethylene terephthalate (PET) and polystyrene (PS). Efforts are made to develop sheets that are suitable for production of sundry goods, such as clear file folders, and molded food containers. Polylactic acid, as well as other general polymer compounds, is easily electrified by friction or the like, and accordingly suffers from damage to appearance caused by adhered dust or deterioration in processability as a result of electrification causing blocking between sheets when used in the form of processed sheets.
Generally available methods to make sheets antistatic include coating sheet surfaces with an antistatic agent and kneading an antistatic agent directly into sheets during an extrusion step.
Japanese Unexamined Patent Publication (Kokai) No. 2002-12687 discloses a technique designed to coat polylactic acid material with an anionic surface active agent and a specific nonionic surface active agent.
Japanese Unexamined Patent Publication (Kokai) No. 2002-114895 discloses a technique designed to mix an electrically conductive agent into polylactic acid material.
Japanese Unexamined Patent Publication (Kokai) N. HEI 10-17757 discloses a technique designed to mix an anionic surface active agent into polylactic acid material.
Japanese Unexamined Patent Publication (Kokai) No. 2004-67801 discloses a technique designed to mix an ionic surface active agent and a nonionic surface active agent into polylactic acid material.
The technique described in JP '687 has some disadvantages. The resulting films tend to have stickiness or suffer from blocking, and coated films will often fail in making a good contact with ink and will not be suitable for printing.
The technique described in JP '895 cannot maintain high transparency though it is a good feature of polylactic acid.
The technique described in JP '757 is designed to increase the decomposition speed of polylactic acid, and cannot serve for maintain antistatic property.
The technique described in JP '801 can provide films with antistatic property, but they are not sufficiently high in blocking resistance, and cannot maintain antistatic property after undergoing a heat history such as thermoforming.
As described above, it is still impossible for the conventional techniques top provide a polylactic acid based resin sheet that is high in antistatic property, transparency, and blocking resistance, and suitable particularly for production of printed moldings.
Thus, in view of such a background, it could be helpful to provide a polylactic acid based resin sheet that is high in antistatic property, transparency, and blocking resistance, and suitable particularly for production of moldings.